1. Field of the Invention
The invention relates to a lens module, more particularly to a lens module with an adjustable lens unit.
2. Description of the Related Art
As shown in FIGS. 1 and 2, Japanese Laid-Open Publication No. 2005-215539 discloses an adjustable lens module for a camera phone. The lens module includes a base 11, an outer covering 12, a driving motor 13, a speed reduction gear system 14 including a plurality of speed reduction gears that are driven rotatably by the driving motor 13, a barrel cam 15 mounted to the base 11 and driven by the speed reduction gear system 14, a first lens unit 16, a second lens unit 17 disposed parallel to the first lens unit 16, and a tension spring (not visible) disposed between the first and second lens units 16 and 17.
The barrel cam 15 includes a cylinder 151 and a spiral portion 152 formed on the surface of the cylinder 151. The spiral portion 152 has an upper spiral surface 153 and a lower spiral surface 154.
The first lens unit 16 includes a first lens frame 161 movably mounted to the base 11, a first lens 162 disposed in the first lens frame 161, and a first cam follower 163 abutting against the upper spiral surface 153 of the barrel cam 15. The second lens unit 17 includes a second lens frame 171 movably mounted to the base 11, a second lens 172 disposed in the second lens frame 171, and a second cam follower 173 abutting against the lower spiral surface 154 of the barrel cam 15. Therefore, the spiral portion 152 of the barrel cam 15 is pressed on both sides by the first and second cam followers 163 and 173.
When the barrel cam 15 rotates about an axis thereof, the first and second cam followers 163 and 173 will slide along the upper and lower spiral surfaces 153 and 154, respectively, and the first and second lens frames 161 and 171 will move toward or away from each other accordingly, thereby resulting in corresponding relative movement between the first and second lenses 162 and 172.
When the driving motor 13 rotates clockwise or counterclockwise, the speed reduction gear system 14 will be driven to rotate simultaneously. Meanwhile, the barrel cam 15 will also be driven to rotate by the speed reduction gear system 14, such that the first and second lenses 162 and 172 are driven to move relative to each other for focus adjustment.
However, the speed reduction gear system 14 has to drive the first and second lens frames 161 and 171 by driving the barrel cam 15 first, rather than driving them directly. Therefore, the number of components and the size of the lens module are difficult to be reduced effectively, which leads to a more complicated assembly process and a higher manufacturing cost.